Storage unit (STU) requirements
Note the following storage unit (STU) requirements for the media servers:
Tape drives are mapped to media servers and these media servers are mapped to STU.
Veritas recommends that you create a single STU, which will include all the media servers and hence all the tape drives. This single STU for all tape outs can be used to create policies. Use the NetBackup JAVA UI to create the STU.
If a robot is used move tape cartridges into and out of tape drives, one of the media servers is assigned a robot controller role. This role is present on only one media server, and doesn't fail over if that media server is down. In such situation, even if the other nodes have connectivity to the tape drives, they can't be used. The media server with the robot control role must be brought online to proceed further.